JPH1163810A - Method and device for manufacturing low purity oxygen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an oxygen power source unit when raw material air is liquefied and rectified to manufacture low purity oxygen. SOLUTION: Raw material air is compressed to a pressure lower than the operation pressure of a high pressure tower 2 and is refined at refining equipment 5 after precooling. Refined raw material air is branched into first and second raw material air. A first raw material is expanded by an expansion turbine 6 and the second raw material air is boosted by a booster 7. The first raw material air cooled by a main heat-exchanger 8 is introduced to a low pressure tower 1 and the second raw material air to a high pressure tower 2 for liquefaction rectification, and product oxygen is recovered from the lower part of the low pressure tower 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for producing low purity oxygen, particularly, by distillation of air at low temperatures, mainly recovered low purity oxygen (99% O ₂ or less) as a product Method and apparatus.

[0002]

2. Description of the Related Art Low-purity oxygen has been conventionally used in the fields of iron and steel, glass melting, etc., but coal gasification combined with depletion of crude oil resources and effective use of energy. Demand for power generation, heavy residue gasification power generation, direct smelting reduction steelmaking, etc. is expected in the future. In these fields, since a large amount of oxygen is consumed, it has been particularly sought to reduce the production cost of oxygen.

As a method for producing low-purity oxygen having a purity of 99% or less, a method is known in which raw air is liquefied and rectified by a double rectification facility having a low-pressure column and a high-pressure column. In this liquefaction rectification method, oxygen is generally extracted in a gaseous or liquid state from the lower part of the low-pressure column, but when producing low-purity oxygen, it is necessary to almost separate oxygen and argon in the recovery part of the low-pressure column. Therefore, the descending liquid and the rising gas in this portion can be reduced as compared with the process for producing high-purity oxygen.

[0004] For this reason, for example, Japanese Patent Application Laid-Open No. 55-3824.
In the method described in Japanese Patent Publication No. 3 (1994), the raw material air is separated into two systems, low pressure and high pressure, and the low pressure raw material air is directly introduced into the low pressure column. As a result, the flow rate of the raw air compressed to a high pressure is reduced, so that the power required for compressing the raw air can be reduced.

[0005] However, in this method, two methods of low pressure and high pressure are used.
The raw material air of the system is compressed by different compressors, and impurities are removed by different purification equipment, which increases equipment costs.In addition, the purification equipment on the low pressure side removes high boiling impurities from the raw air. Requires a large amount of energy and increases the power required for the apparatus.

In the method described in Japanese Patent Application Laid-Open No. 5-296652, after purifying by compressing the entire amount of raw air to a pressure corresponding to the operating pressure of the high-pressure column, a part of the raw air is branched. Then, the compressed air is expanded by an expansion turbine to obtain low-pressure raw material air, and the power obtained by the expansion is used as compression power for the raw material air.

In this method, the work obtained by the expansion in the expansion turbine is used as a part of the power for compressing the raw air, and the power is recovered. However, the energy obtained by the expansion of the fluid is expanded. All of this energy could not be used as compression energy because it would decrease due to the efficiency of the turbine or compressor. Also, the low-pressure feed air introduced into the low-pressure tower is once compressed to the pressure of the high-pressure tower and then expanded by the expansion turbine, but the work due to this expansion is merely used as the compression power of the compressor, It is more efficient to compress the low-pressure feed air introduced into the low-pressure column to a pressure lower than the pressure in the high-pressure column.

Accordingly, an object of the present invention is to provide a method and an apparatus for producing low-purity oxygen that can reduce the unit cost of oxygen power and the production cost as compared with the above-described processes.

[0009]

Means for Solving the Problems To achieve the above object, the method for producing low-purity oxygen of the present invention is characterized in that the raw air is liquefied and rectified by a double rectification facility having a low-pressure column and a high-pressure column. In the method for producing oxygen, a step of compressing the feed air to a pressure lower than the operating pressure of the high-pressure column,
A step of pre-cooling the compressed raw air, a step of purifying by removing impurities such as moisture and carbon dioxide from the pre-cooled raw air, and a step of branching the purified raw air into a first raw air and a second raw air, and branching. A step of expanding the first raw material air, a step of increasing the pressure of the branched second raw material air, and a heat exchange of the expanded first raw material air and the raised second raw air with a fluid obtained by liquefaction rectification. Cooling, and the cooled first
A step of introducing raw material air into the low-pressure column and a step of introducing cooled second raw material air into the high-pressure column to separate into oxygen and nitrogen by liquefaction rectification, and the lower part of the low-pressure column obtained by liquefaction rectification And recovering at least a part of the oxygen as a product.

Further, in the method for producing low-purity oxygen according to the present invention, the pressure of the second raw material air is increased by using the work of expansion of the first raw material air. Heating, cooling before pressurizing the second raw material air, the product oxygen compresses liquefied oxygen at the lower part of the low-pressure column obtained by liquefaction rectification, and then a part of the second raw material air. Of the second raw material air that exchanges heat with the liquefied oxygen after liquefaction by the heat exchange, and then at least one theoretical line from the introduction position of the second raw material air in the high-pressure column. It is characterized in that it is introduced into the high-pressure column at a position above the stage.

[0011] The apparatus for producing low-purity oxygen of the present invention comprises:
In a device for producing low-purity oxygen by liquefying and rectifying raw material air in a double rectification facility having a low-pressure column and a high-pressure column, a raw material air compressor that compresses raw material air, and a pre-cooling device that pre-cools compressed raw material air A purification facility for purifying by removing impurities such as moisture and carbon dioxide from pre-cooled raw material air;
An expansion turbine that expands a part of the purified raw air, a booster that pressurizes the remainder of the purified raw air, and a fluid obtained by liquefying the expanded first raw air and the raised second raw air. A main heat exchanger for cooling by heat exchange, a path for introducing the cooled first raw material air to the low pressure column, a path for introducing the cooled second raw material air to the high pressure column, and a lower part of the low pressure column by liquefaction rectification. And a path for recovering at least a part of the generated oxygen as a product.

Further, in the apparatus for producing low-purity oxygen of the present invention, the expansion turbine and the booster are coaxially connected, and the purified raw material air to be expanded by the expansion turbine is heated before being expanded. A heat exchanger, wherein the booster inhales purified air at a temperature between the hot end temperature and the cold end temperature in the main heat exchanger and increases the pressure, and the oxygen is a product. A pump for compressing liquefied oxygen at the bottom of the low-pressure column obtained by liquefied rectification, and heat exchange between the liquefied oxygen compressed by the pump and a part of the second raw material air to convert liquefied oxygen An oxygen evaporator for evaporating and liquefying the second raw material air;
A path for introducing the second raw material air liquefied by the oxygen evaporator into the high-pressure column at a position at least one theoretical stage higher than the high-pressure column introduction position of the second raw material air that does not pass through the oxygen evaporator; At least one of the low-pressure column and the high-pressure column is a packed rectification column.

[0013]

FIG. 1 is a system diagram showing one embodiment of the low-purity oxygen producing apparatus of the present invention. This low-purity oxygen production apparatus is an apparatus for producing low-purity oxygen by liquefying raw air in a double rectification facility having a low-pressure column 1 and a high-pressure column 2, and is a raw air compression system for compressing the raw air. Machine 3, pre-cooling equipment 4 for pre-cooling compressed raw air, purification equipment 5 for removing impurities such as moisture and carbon dioxide from the pre-cooled raw air, expansion turbine 6 for expanding a part of the purified raw air, purified raw material It has a booster 7 for increasing the pressure of the remainder of the air, a main heat exchanger 8 for cooling the expanded first raw material air and the pressurized second raw material air by heat exchange with a fluid obtained by liquefaction rectification, and the like. The low-purity oxygen gas of the product is recovered from the lower part of the low-pressure column 1.

Hereinafter, the operating pressure of the low pressure column 1 is set to 1.4 kg /
cm ² abs, operating pressure of the high pressure column 2 is 5.6 kg / cm
^{The case where 2} abs is used and the product oxygen gas is collected at 22355 Nm ³ / h will be described as an example.

First, 10210 introduced from the path 50
The feed air of 0 Nm ³ / h is compressed by the feed air compressor 3 to 4.9 kg / cm ² abs, which is lower than the operating pressure of the high-pressure column 2 and higher than the operating pressure of the low-pressure column 1, and led out to the path 51. You. This compressed raw air passes through the heat exchanger 11 from the path 51, is further introduced into the precooling equipment 4 from the path 52, is precooled, and is introduced into the purification equipment 5 through the path 53.

The purified raw material air is purified by removing impurities such as moisture and carbon dioxide in the purifying equipment 5, and the purified raw material air led out to the path 54 is branched into a first raw material air in a path 55 and a second raw material air in a path 56. I do. 25000Nm branched to route 55
^{The 3} / h first raw material air is heat-exchanged with the compressed raw material air in the heat exchanger 11 and heated to 130 ° C.
7, flows into the expansion turbine 6, and expands to 1.5 kg / cm ² abs corresponding to the operating pressure of the low-pressure tower 1. The first raw material air that has been expanded to a low pressure flows into the main heat exchanger 8 through a path 58, and is cooled by heat exchange with a fluid obtained by liquefaction rectification, that is, oxygen gas and nitrogen gas, It is introduced into the middle stage of the low-pressure column 1 via the paths 59 and 60.

77100 Nm ³ / h branched to the path 56
5.7 kg corresponding to the operating pressure of the high pressure tower 2 by the work obtained by the expansion of the first raw material air by the booster 7 coaxially connected to the expansion turbine 6.
/ Cm ² abs, cooled by the aftercooler 12, and led out to the path 61. 5800 Nm ³ / h of the pressurized first raw material air is branched from a path 61 to a path 62 to form a third flow, and the blower 13 supplies 8.7 kg / h.
After being compressed to cm ² abs, the aftercooler 14,
It flows into the main heat exchanger 8 via the path 63. This third raw material air is supplied to a path 6 at a position of -90 ° C. in the middle of the main heat exchanger 8.
4 and expanded by the expansion turbine 15 for generating cold.
Expands to kg / cm ² abs and generates the refrigeration required to operate the device. It expands in the expansion turbine 15 to a low pressure,
The third raw material air led out to the path 65 merges with the second raw material air in the path 59, and has a total flow rate of 30,800 Nm ³ / h.
And flows into the low pressure column 1 from the path 60.

On the other hand, the second traveling from the route 61 to the route 66
The raw material air 71300 Nm ³ / h is cooled to a temperature near the dew point in the main heat exchanger 8,
Introduced at the bottom. The second raw material air is condensed in the main condensing evaporator 16 and liquefied and rectified by gas-liquid contact with a reflux liquid flowing down in the high-pressure column 2. The nitrogen gas at the top of the column and the oxygen content at the bottom of the column are enriched. Separated into liquefied air. The nitrogen gas is introduced into the main condenser evaporator 16 from the top of the tower and condensed, and a part of the condensed liquefied nitrogen is supplied to the passage 68 and the subcooler 17.
After the pressure is reduced to the pressure of the low-pressure column 1 by the valve 18 via the valve 18, the pressure is introduced into the upper part of the low-pressure column 1. The liquefied air extracted from the bottom of the tower to the path 69 is depressurized to the pressure of the low-pressure tower 1 by the valve 20 via the subcooler 19, and then introduced into the middle stage of the low-pressure tower 1.

In the low-pressure column 1, the first raw material air, the third raw material air rising in the low-pressure column 1 and the gas evaporated in the main condensation evaporator 16 are combined with the liquefied nitrogen and liquefied air flowing down in the column. The rectification is carried out by gas-liquid contact to separate into nitrogen gas at the top of the column and liquefied oxygen at the bottom of the column. Nitrogen gas 79445 Nm ³ / h is extracted from the path 70 at the top of the tower, and from the path 71 at the bottom of the tower. A part of the oxygen gas evaporated in the main condensing evaporator 16 is extracted at 22355 Nm ³ / h. The nitrogen gas extracted from the top of the tower to the path 70 is supplied to the subcooler 17,1.
9 and the main heat exchanger 8 through the path 72, exchanges heat with the raw material air and is led out to the path 73, and a part of the
After being branched to 4 and passed through the regeneration heater 21 to be used for regeneration of the refining equipment 5, it is discharged from the path 75. Further, the remaining nitrogen gas can be collected as a product as needed. Then, the oxygen gas extracted to the path 71 is
The main heat exchanger 8 exchanges heat with the raw material air to raise the temperature to 12 ° C.
It is recovered as product oxygen from the passage 76.

As described above, in producing low-purity oxygen, the raw air is compressed to a pressure lower than the pressure of the high-pressure column 2 and purified, whereby the system from the raw air compressor 3 to the purification facility 5 is purified. Since it can be unified, the initial cost can be reduced as compared with the conventional method of compressing and refining the raw material air by two systems of high pressure and low pressure, and it is not necessary to remove impurities from the low pressure raw material air. Can be reduced.

Further, since all of the raw material air is not compressed to the pressure of the high-pressure column 2, the compression ratio and expansion ratio when compressing and expanding the low-pressure raw material air supplied to the low-pressure column 1 are reduced, and the mechanical loss is reduced. Can be reduced. In particular, an expansion turbine 6 for expanding the low-pressure side raw material air and a booster 7 for raising the high-pressure side raw material air are coaxially connected to each other.
By increasing the pressure of the high-pressure side raw material air using the work due to the expansion of the raw material air, the second raw material air can be efficiently raised, and effective use of energy can be achieved. Further, the first raw material air is heated by the heat exchanger 11 and then introduced into the expansion turbine 6 and expanded, whereby the first raw material air can be efficiently expanded. By increasing the temperature difference from the raw material air, the compression ratio in the booster 7 can be increased.

When the low-purity oxygen is produced as described above, the unit oxygen power consumption is 0.34 kWh / Nm ³ , which can be reduced by about 10% as compared with the conventional process.

Further, oxygen can be extracted from the lower part of the low-pressure column 1 with a liquid. In this case, as shown by the broken line in FIG. 1, liquefied oxygen is extracted from the lower part of the low-pressure column to the path 76, and the difference between the boiling point of the liquefied oxygen and the boiling point of the second raw material air used as a heating source is supplied by the liquefied oxygen pump 22. Is compressed to a pressure at which it reaches an appropriate temperature and introduced into the oxygen evaporator 23, and a part of the second raw material air flowing through the path 67 is branched into a path 77 and introduced into the oxygen evaporator 23 as a heating source. The oxygen gas evaporated by the heat exchange with a part of the second raw material air in the oxygen evaporator 23 is introduced into the main heat exchanger 8 through the passage 78,
The temperature is raised by exchanging heat with the raw material air and collected from the passage 76. In addition, the second raw material air liquefied by heat exchange with liquefied oxygen in the oxygen evaporator 23 passes through the path 79 and the valve 24, and is at least one theoretical path from the position where the second raw material air that does not pass through the oxygen evaporator 23 is introduced into the high pressure column. It is introduced into the high-pressure column 2 at a position above the stage.

As described above, by extracting oxygen from the low-pressure column 1 with a liquid, the purity of the liquefied oxygen stored at the bottom of the low-pressure column 1 is reduced by one compared to the case of directly extracting oxygen gas from the low-pressure column 1. The pressure can be lowered by the equilibrium stage, and the temperature difference in the main condensation evaporator 16 can be made large, so that the pressure in the high-pressure column 2 can be lowered. The liquefied oxygen can be pressurized by its own position head without using the liquefied oxygen pump 22.

Further, the liquefied second raw material air is introduced at least one theoretical stage from the position where the second raw material air is introduced without passing through the oxygen evaporator 23, so that the high-pressure raw material air supply stage and the liquefied air supply stage are separated. Since the reflux ratio L / V (ratio of descending liquid to ascending gas) approaches 1, the separation by rectification can be promoted.

FIG. 2 is a system diagram showing another embodiment of the present invention, in which the pressure of the second raw material air is increased by low-temperature compression. Note that the same components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Hereinafter, similarly to the above, the operating pressure of the low pressure column 1 is set to 1.4 kg / c.
m ² abs, operating pressure of the high pressure column 2 is 5.6 kg / cm ²
The case where abs is used and the product oxygen is collected at 22355 Nm ³ / h will be described.

The feed air of 102100 Nm ³ / h from the passage 50 is fed to the feed air compressor 3 at 4.9 kg / cm ² a
bs, is introduced into the refining facility 5 through the path 51, the pre-cooling equipment 4, and the path 53, is purified, and is led out to the path 54. The purified raw air in the passage 54 is branched into a third raw air for generating cold in the passage 80, a first raw air for low pressure in the passage 81, and a second raw air for high pressure in the passage 82.

First raw material air 25200 Nm ^{3 in} path 81
/ H expands to 1.4 kg / cm ² abs in the expansion turbine 6 and becomes low in temperature, flows into the middle part of the main heat exchanger 8 through the path 83, is cooled, and is led out to the path 84. In addition, the second raw material air 71620 Nm ³ /
h is cooled to the intermediate temperature in the main heat exchanger 8 and then introduced into the booster 7 through the path 85 to be 5.7 kg / cm ² a
bs, is again introduced into the main heat exchanger 8 by the path 86, is cooled, and is introduced into the lower part of the high-pressure column 2 via the path 67.

The third raw air 5280Nm ³ /
h is heated in the heat exchanger 25, is compressed to 6.9 kg / cm ² abs by the blower 13 through the path 87, is cooled through the after cooler 14, the path 88, and the heat exchanger 25, and is then cooled. It is introduced into the main heat exchanger 8 by 89. The third raw material air cooled to −100 ° C. in the main heat exchanger 8 is led out to the path 64 in the same manner as described above and introduced into the expansion turbine 15 for generating cold, and 1.4 kg / cm ² abs.
To generate cold, and through the path 65, the path 8
4 and is introduced into the middle stage of the low-pressure column 1 via the path 60.

Then, the low-pressure column 1 and the high-pressure column 2
As a result, the nitrogen gas 79445 Nm ³ / h is extracted from the passage 70 at the top of the low-pressure column 1 and is led out to the passage 73 via the main heat exchanger 8. Further, oxygen gas 22355 Nm ³ / h is extracted from the lower passage 71 of the low-pressure column 1 and recovered from the passage 76 via the main heat exchanger 8. Alternatively, liquefied oxygen is extracted from the lower passage 76 of the low-pressure tower 1, evaporated in the oxygen evaporator 23, and recovered from the passage 76 via the main heat exchanger 8. The unit oxygen power consumption in this embodiment was also 0.34 kWh / Nm ^3, which was the same as in the above embodiment.

As shown in this embodiment, the booster 7 driven by the expansion turbine 6 has a low-temperature specification, and the pressure of the second raw material air is raised at a low temperature. be able to. In addition, in order to obtain a temperature difference between the first raw material air and the second raw material air, in the above-described embodiment, the first raw material air introduced into the expansion turbine 6 is heat-exchanged with the compressed raw material air by the heat exchanger 11 to rise. Although a relatively large-capacity heat exchanger was installed because of the temperature, in the present embodiment, the temperature difference was obtained by cooling the second raw material air with the main heat exchanger 8, so The exchanger 11 can be omitted. Although the heat exchanger 25 for the same purpose is installed in the path of the third raw material air, the flow rate of the third raw material air is small, so that the heat exchanger 25 can be much smaller than the heat exchanger 11. .

Further, the unit oxygen power consumption in each embodiment is a numerical value when each rectification column is formed in a tray type using a perforated plate tray, and both rectification columns or a low pressure column and a high pressure column are used. When either one of the packed rectification column,
Since the pressure loss is smaller than that of the shelf type, a greater power reduction effect can be obtained.

[0033]

As described above, according to the method and apparatus for producing low-purity oxygen of the present invention, in the purification facility, the raw material air is made into one system, and thereafter, is branched into high-pressure and low-pressure raw material air. And the initial cost of a raw material air compressor can be reduced. Further, since there is no need to remove impurities from the low-pressure air, the power required for this can be reduced. further,
Since all of the raw air is not compressed to the pressure of the high-pressure column, mechanical loss due to compression and expansion of the air supplied to the low-pressure column can be reduced. Therefore, low-purity oxygen can be produced at lower cost than before.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a low-purity oxygen production apparatus of the present invention.

FIG. 2 is a system diagram showing another embodiment of the low-purity oxygen production apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Low-pressure tower, 2 ... High-pressure tower, 3 ... Raw material air compressor, 4 ... Pre-cooling equipment, 5 ... Refining equipment, 6 ... Expansion turbine, 7 ... Pressure booster, 8 ... Main heat exchanger, 11 ... Heat exchanger, 13: blower, 15: expansion turbine for generating cold, 16: main condensing evaporator, 17, 19: subcooler, 21: heater for regeneration, 22
... liquefied oxygen pump, 23 ... oxygen evaporator, 25 ... heat exchanger

Claims (12)

[Claims] 1. A method for producing low-purity oxygen by liquefying raw air in a double rectification facility having a low-pressure column and a high-pressure column, wherein the raw air is compressed to a pressure lower than the operating pressure of the high-pressure column. A step of pre-cooling the compressed raw air, a step of purifying by removing impurities such as moisture and carbon dioxide from the pre-cooled raw air, and branching the purified raw air into a first raw air and a second raw air. A step of expanding the branched first raw material air, a step of increasing the pressure of the branched second raw material air, and a step of converting the expanded first raw material air and the raised second raw air to a fluid obtained by liquefaction rectification. And cooling the first raw material air cooled in the low-pressure column,
A step of introducing the cooled second raw material air into the high-pressure column to separate into oxygen and nitrogen by liquefaction rectification, and converting at least a portion of the oxygen at the lower part of the low-pressure column obtained by liquefaction rectification into a product And recovering as low purity oxygen. 2. The method for producing low-purity oxygen according to claim 1, wherein the step of increasing the pressure of the second raw material air is performed by utilizing work caused by expansion of the first raw material air. 3. The method for producing low-purity oxygen according to claim 1, wherein the first raw material air is heated before being expanded. 4. The method for producing low-purity oxygen according to claim 1, wherein the second raw material air is cooled before the pressure is increased. 5. The method according to claim 1, wherein the recovery of the product oxygen is performed by compressing liquefied oxygen obtained in the liquefaction rectification at the lower part of the low-pressure column and evaporating the compressed oxygen by heat exchange with a part of the second raw material air. The method for producing low-purity oxygen according to claim 1, wherein: 6. A part of the second raw material air which exchanges heat with the liquefied oxygen is liquefied by the heat exchange, and then is pressurized at a position at least one theoretical stage higher than the introduction position of the second raw material air in the high pressure column. 6. The method according to claim 5, wherein the gas is introduced into a tower.
The method for producing low-purity oxygen according to the above. 7. An apparatus for producing low-purity oxygen by liquefying raw air in a double rectification facility having a low-pressure tower and a high-pressure tower, wherein a raw air compressor for compressing the raw air, a compressed air for the raw air, Pre-cooling equipment for pre-cooling, purification equipment for purifying by removing impurities such as moisture and carbon dioxide from pre-cooled raw air, expansion turbine for expanding a part of the purified raw air, and pressurizing for boosting the remainder of the purified air A main heat exchanger for cooling the expanded first raw material air and the pressurized second raw material air by heat exchange with a fluid obtained by liquefaction rectification, and the cooled first raw material air to the low-pressure column. A path for introducing, a path for introducing the cooled second raw material air into the high-pressure column, and a path for recovering at least a part of oxygen generated at the lower part of the low-pressure column by liquefaction rectification as a product. And low net Degree oxygen production equipment. 8. The apparatus for producing low-purity oxygen according to claim 7, wherein the expansion turbine and the booster are coaxially connected. 9. The apparatus for producing low-purity oxygen according to claim 7, further comprising a heat exchanger for heating the purified air to be expanded by the expansion turbine before the air is expanded. 10. The pressure booster according to claim 7, wherein the pressure of the purified raw material air is increased at a temperature between the hot end temperature and the cold end temperature in the main heat exchanger. Low purity oxygen production equipment. 11. A path for recovering the oxygen as a product includes a pump for compressing liquefied oxygen at the bottom of the low-pressure column obtained by liquefaction rectification, and a part of the liquefied oxygen compressed by the pump and a part of the second raw material air. And an evaporator for evaporating liquefied oxygen by exchanging heat with liquefied second raw material air,
A path for introducing the second raw material air liquefied by the oxygen evaporator into the high-pressure column at a position at least one theoretical stage above the high-pressure column introduction position of the second raw material air that does not pass through the oxygen evaporator. The apparatus for producing low-purity oxygen according to claim 7, characterized in that: 12. The apparatus for producing low-purity oxygen according to claim 7, wherein at least one of the low-pressure column and the high-pressure column is a packed rectification column.